The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
To reduce the quantity of undesirable particulate matter and nitrogen oxide (NOx) emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment systems have been developed. A need for exhaust aftertreatment systems particularly may arise when diesel combustion processes are implemented.
One method used to reduce NOx emissions from internal combustion engines is known as selective catalytic reduction (SCR). SCR may include injecting a reagent into the exhaust stream of the engine to form a reagent and exhaust gas mixture that is subsequently passed through a reactor containing a catalyst. The catalyst is capable of reducing the NOx concentration in the presence of the reagent. For example only, the catalyst may include activated carbon or metals, such as platinum, vanadium, or tungsten. An aqueous urea solution is known to be an effective reagent in SCR systems for diesel engines.
Exhaust aftertreatment systems that use SCR include at least a pump to circulate the reagent and an injector to deliver the reagent into the exhaust stream. Aftertreatment systems require the delivery components, e.g. the injectors, to be cooled. Some aftertreatment systems use the reagent to cool the delivery components. As an example, the injector may have both a delivery flow and a return flow. The pump continuously circulates the reagent through the injector. When the injector is actuated, reagent is injected into the exhaust gas, i.e. delivery flow, and circulates back to the pump via a holding tank, i.e. return flow. When the injector is not actuated, the reagent only circulates back to the pump via the holding tank.
There is a need to accurately determine the flow of reagent that is injected into the exhaust stream.